When fabricating parts from metal sheet in low-production runs, incremental sheet forming (ISF) is an advantageous process. To improve the strength of the finished parts, the use of naturally aging alloys, such as certain alloys of aluminum, may be contemplated. However, since the hardness of the workpiece material increases in a relatively short time period due to the natural aging of such alloys, the window available for ISF operations may be insufficient, especially when complicated parts are being formed. ISF may therefore be limited in its ability to produce large and/or complicated parts when alloys, which harden due to natural aging, are utilized.